The present invention relates to image region of interest encoding.
Image compression is minimizing the size in bytes of a graphics file without degrading the quality of the image to an unacceptable level. The reduction in file size allows more images to be stored in a given amount of disk or memory space. It also reduces the time required for images to be sent over the Internet or downloaded from Web pages.
There are several different standards that define the ways in which image files can be compressed. Three common standards, for example, are the Joint Photographic Experts Group (JPEG) standard, the JPEG2000 standard and the Graphics Interchange Format (GIF) standard.
The JPEG2000 digital image compression standard, for example, allows the compression of an arbitrary region of interest (e.g., foreground) within an image to be compressed at a higher quality than the remainder of the image (e.g., background). The JPEG2000 digital image standard uses the “max shift” method in conjunction with a post compression rate distortion (PCRD) optimization. In the max shift method, an image is first transformed into a wavelet domain and a subset of coefficients that contribute to a foreground are determined. The foreground coefficients are “left shifted” so that the modified foreground coefficients are larger than the largest possible background coefficient.
A decoder can now identify whether a coefficient belongs to the foreground or background by simply looking at its value. The coefficients of the foreground are now very large numbers and hence an error occurring in these coefficients is penalized by a large distortion. The PCRD optimization ensures that these foreground coefficients are included prior to background coefficients, which ensures that a large part of the bit budget is given to the encoding of the foreground coefficients.